From: Adam Kropelin Adds a kernel boot parameter "lpj=NNN" which allows the operator to specify the loops-per-jiffy value. This shaves up to a quarter of a second off boot times, which are critical for embedded appliances. It's a bit thin, but the code is in __init. Signed-off-by: Adam Kropelin Signed-off-by: Andrew Morton --- 25-akpm/Documentation/kernel-parameters.txt | 14 +++ 25-akpm/init/main.c | 111 +++++++++++++++++----------- 2 files changed, 85 insertions(+), 40 deletions(-) diff -puN Documentation/kernel-parameters.txt~preset-loops_per_jiffy-for-faster-booting Documentation/kernel-parameters.txt --- 25/Documentation/kernel-parameters.txt~preset-loops_per_jiffy-for-faster-booting 2004-07-11 21:49:04.115252032 -0700 +++ 25-akpm/Documentation/kernel-parameters.txt 2004-07-11 21:49:04.121251120 -0700 @@ -574,6 +574,20 @@ running once the system is up. so, the driver will manage that printer. See also header of drivers/char/lp.c. + lpj=n [KNL] + Sets loops_per_jiffy to given constant, thus avoiding + time-consuming boot-time autodetection (up to 250 ms per + CPU). 0 enables autodetection (default). To determine + the correct value for your kernel, boot with normal + autodetection and see what value is printed. Note that + on SMP systems the preset will be applied to all CPUs, + which is likely to cause problems if your CPUs need + significantly divergent settings. An incorrect value + will cause delays in the kernel to be wrong, leading to + unpredictable I/O errors and other breakage. Although + unlikely, in the extreme case this might damage your + hardware. + ltpc= [NET] Format: ,, diff -puN init/main.c~preset-loops_per_jiffy-for-faster-booting init/main.c --- 25/init/main.c~preset-loops_per_jiffy-for-faster-booting 2004-07-11 21:49:04.117251728 -0700 +++ 25-akpm/init/main.c 2004-07-11 21:49:04.123250816 -0700 @@ -178,15 +178,28 @@ static int __init obsolete_checksetup(ch return 0; } -/* this should be approx 2 Bo*oMips to start (note initial shift), and will - still work even if initially too large, it will just take slightly longer */ +static unsigned long preset_lpj; +static int __init lpj_setup(char *str) +{ + preset_lpj = simple_strtoul(str,NULL,0); + return 1; +} + +__setup("lpj=", lpj_setup); + +/* + * This should be approx 2 Bo*oMips to start (note initial shift), and will + * still work even if initially too large, it will just take slightly longer + */ unsigned long loops_per_jiffy = (1<<12); EXPORT_SYMBOL(loops_per_jiffy); -/* This is the number of bits of precision for the loops_per_jiffy. Each - bit takes on average 1.5/HZ seconds. This (like the original) is a little - better than 1% */ +/* + * This is the number of bits of precision for the loops_per_jiffy. Each + * bit takes on average 1.5/HZ seconds. This (like the original) is a little + * better than 1% + */ #define LPS_PREC 8 void __devinit calibrate_delay(void) @@ -194,40 +207,53 @@ void __devinit calibrate_delay(void) unsigned long ticks, loopbit; int lps_precision = LPS_PREC; - loops_per_jiffy = (1<<12); + if (preset_lpj) { + loops_per_jiffy = preset_lpj; + printk("Calibrating delay loop (skipped)... " + "%lu.%02lu BogoMIPS preset\n", + loops_per_jiffy/(500000/HZ), + (loops_per_jiffy/(5000/HZ)) % 100); + } else { + loops_per_jiffy = (1<<12); - printk("Calibrating delay loop... "); - while ((loops_per_jiffy <<= 1) != 0) { - /* wait for "start of" clock tick */ - ticks = jiffies; - while (ticks == jiffies) - /* nothing */; - /* Go .. */ - ticks = jiffies; - __delay(loops_per_jiffy); - ticks = jiffies - ticks; - if (ticks) - break; - } + printk("Calibrating delay loop... "); + while ((loops_per_jiffy <<= 1) != 0) { + /* wait for "start of" clock tick */ + ticks = jiffies; + while (ticks == jiffies) + /* nothing */; + /* Go .. */ + ticks = jiffies; + __delay(loops_per_jiffy); + ticks = jiffies - ticks; + if (ticks) + break; + } + + /* + * Do a binary approximation to get loops_per_jiffy set to + * equal one clock (up to lps_precision bits) + */ + loops_per_jiffy >>= 1; + loopbit = loops_per_jiffy; + while (lps_precision-- && (loopbit >>= 1)) { + loops_per_jiffy |= loopbit; + ticks = jiffies; + while (ticks == jiffies) + /* nothing */; + ticks = jiffies; + __delay(loops_per_jiffy); + if (jiffies != ticks) /* longer than 1 tick */ + loops_per_jiffy &= ~loopbit; + } -/* Do a binary approximation to get loops_per_jiffy set to equal one clock - (up to lps_precision bits) */ - loops_per_jiffy >>= 1; - loopbit = loops_per_jiffy; - while ( lps_precision-- && (loopbit >>= 1) ) { - loops_per_jiffy |= loopbit; - ticks = jiffies; - while (ticks == jiffies); - ticks = jiffies; - __delay(loops_per_jiffy); - if (jiffies != ticks) /* longer than 1 tick */ - loops_per_jiffy &= ~loopbit; + /* Round the value and print it */ + printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", + loops_per_jiffy/(500000/HZ), + (loops_per_jiffy/(5000/HZ)) % 100, + loops_per_jiffy); } -/* Round the value and print it */ - printk("%lu.%02lu BogoMIPS\n", - loops_per_jiffy/(500000/HZ), - (loops_per_jiffy/(5000/HZ)) % 100); } static int __init debug_kernel(char *str) @@ -249,8 +275,10 @@ static int __init quiet_kernel(char *str __setup("debug", debug_kernel); __setup("quiet", quiet_kernel); -/* Unknown boot options get handed to init, unless they look like - failed parameters */ +/* + * Unknown boot options get handed to init, unless they look like + * failed parameters + */ static int __init unknown_bootoption(char *param, char *val) { /* Change NUL term back to "=", to make "param" the whole string. */ @@ -261,8 +289,10 @@ static int __init unknown_bootoption(cha if (obsolete_checksetup(param)) return 0; - /* Preemptive maintenance for "why didn't my mispelled command - line work?" */ + /* + * Preemptive maintenance for "why didn't my mispelled command + * line work?" + */ if (strchr(param, '.') && (!val || strchr(param, '.') < val)) { printk(KERN_ERR "Unknown boot option `%s': ignoring\n", param); return 0; @@ -302,7 +332,8 @@ static int __init init_setup(char *str) unsigned int i; execute_command = str; - /* In case LILO is going to boot us with default command line, + /* + * In case LILO is going to boot us with default command line, * it prepends "auto" before the whole cmdline which makes * the shell think it should execute a script with such name. * So we ignore all arguments entered _before_ init=... [MJ] _